Warburg first discovered the thermo-magnetic effect in 1881. Warburg found that by placing selected materials in a magnetic field resulted in a temperature increase. Likewise, removing selected materials from the magnetic field causes a reduction in temperature. Thereafter a lot of effort has been devoted to exploring possible applications for the interaction of electromagnetic and thermal energy. Results of the thermo-magnetic effect vary greatly depending on the method of generating the magnetic field, selection of magnetocaloric material and operating procedures. A magnetic refrigeration apparatus is the most tangible application.
Reference found in U.S. Pat. No. 4,916,907 in 1990 to Munk et al, which discloses a magnetic inductor equipped with permanent magnets. However, it does not provide a complete and specific application for the magnetic refrigeration apparatus. U.S. Pat. No. 6,526,759 discloses a design for the magnetic refrigeration apparatus. It mainly uses thermal piping coupled with the difference of thermal spots and adopts a rotating operation to complete thermal circulation. U.S. Pat. No. 4,107,935 discloses a magnetic refrigerator that uses rotating magnetic material. It has a pump to deliver working fluid to a specially designed rotating thermo-magnetic apparatus. The thermo-magnetic apparatus contains magnetocaloric material and rotates continuously in one direction between a strong magnetic field and a weak magnetic field. The working fluid pumps through a complex flow path in the rotating thermo-magnetic apparatus to perform heat exchange with the magnetocaloric material for magnetic refrigeration.
Studies and research related to the thermo-magnetic effect show that magnetic field intensity and magnetic field control are areas that require more work. Permanent magnets are gradually replacing super-conducted material as the magnetic source and can simplify the design of low temperature operating environment. However, most permanently magnetic material used at present have a magnetic intensity of less than 1.5 Tesla. This is not adequate for most magnetic refrigeration applications.